Hibiscus fungal disease guide
There’s no more commanding species of shrubbery with which to adorn your garden than hibiscus. Unfortunately, humans aren’t the only organisms that love the larger-than-life flowers and beguiling colors of the many faces of hibiscus. In the guide below, we’ll take you through all the fungal diseases that wish to do your hibiscus harm.
We’ll discuss what each disease is, how it occurs, and how to treat or prevent it, where possible. By the end of this article, you should be even more prepared to handle anything that nature can throw at your hibiscus shrub. Let’s get started, shall we?
Types of hibiscus fungal diseases
There are more fungal diseases that affect hibiscus than we know what to do with. However, to keep our guide short and sweet, we’re going to be looking at five of the most commonly occurring fungal diseases.
The great thing about these diseases is that because they’re all fungal, they most likely have similar causes and treatments to the various other types of fungal diseases. This means that no matter what fungal disease your hibiscus has, it’s likely that the remedy for one of these five diseases will work to eradicate it and save your plant.
Armillaria root rot
This particular fungal disease is caused by an organism known as oak root fungus. This name oddly has nothing to do with where the fungus is found, though, as oak root fungus has no specificity for oak trees. It does, however, love hibiscus shrubs. Even though the common name for this particular critter is oak root fungus, it gets its official name from the fungal genus to which it belongs, Armillaria.
How does Armillaria root rot work?
This is an incredibly dangerous fungal disease in terms of your hibiscus’ survival. Essentially, the Armillaria starts its assault by attacking what we call the vascular cambium. This is the tissue in the tree that generates wood and bark.
This tissue originates in the young roots of your hibiscus plant, and this is where the fungal infection starts as well. From the roots, the rot will spread literally to your hibiscus’ main stem. In the most severe cases, the infection will then surround the base of the trunk and result in the death of your entire shrub.
The destruction doesn’t stop there, though. Unfortunately, Armillaria is not just a pathogen that kills off your hibiscus shrub’s living tissue. It’s also a saprobe. This means that once your shrub dies, Armillaria simply continues thriving off of the dead and decaying tissue.
This double-edged sword is made even sharper by the fact that the propagules of this particular fungus can live underground for decades as mycelium even after the host hibiscus is dead. Honestly, we’re starting with the big bad of hibiscus fungal diseases here, and it’s an absolute belter to deal with.
How to identify Armillaria root rot
The easiest way to tell whether your hibiscus has a fungal disease infection is to look for the presence of mushrooms around your plant. These will be fairly close to the base of the plant, and could even be on the bark itself. In the case of Armillaria root rot, you’re looking for little brown mushrooms known as honey mushrooms.
Please note that this name is simply due to the slightly golden-brown color, and is not attributed to the taste. Please don’t eat random mushrooms found in your garden, even if they sound delectable.
It’s pertinent to note, however, that honey mushrooms don’t always grow where Armillaria root rot sets in. Unfortunately, you’ll need to look out for more consistent signs. One of these is the presence of mycelial fans. These are structures that grow and spread underneath the bark.
You may be able to see these structures where the bark has fallen from your hibiscus shrub, but in cases where you suspect a presence of Armillaria root rot, you may need to remove portions of dead bark to inspect your hibiscus shrub more closely. These fans are primarily white or cream in color, and spread forward and outward over the subsurface of your hibiscus shrub.
Another good way to tell whether your hibiscus shrub is being plagued by Armillaria root rot is to look for black rhizomorphs. Rhizomorphs are threadlike structures that typically make up the body of many species of fungus. These are primarily used for the absorption and transportation of nutrients. Unfortunately, rhizomorphs are sometimes very difficult to identify because they look like fine roots. However, these are usually darker and smoother than roots.
In most cases, you won’t find mushrooms, rhizomorphs or mycelial fans, simply because they’re all difficult to spot. These fungi are incredibly well-adapted to moving through the shadows without detection. The truth of the matter is that unless you pay really close attention to your plants, you won’t identify Armillaria fungi until they result in root rot or other physical damage. By this time, it’s usually too late.
How to manage Armillaria root rot
The good news is that in some cases you won’t need to do anything to protect your plants from Armillariaroot rot as many plants are completely immune to the effects of the fungus. Unfortunately, this is not one of those cases, hibiscus isn’t one of those plants, and if this fungus takes root in your plants you will likely have your hands full for a while.
The first type of management we’ll discuss first is prevention. The easiest way to prevent Armillaria root rot is to keep your plants in a low-stress environment. In this case, a low-stress environment means that your plant needs to be thriving without environmental stresses. These stresses would amount to excess or inadequate irrigation, inadequate temperatures, and not enough or too much sunlight.
Other things that would count as environmental stresses are broken or damaged roots. Simply put, the easiest way to ensure that your hibiscus plants are safe is to take care of them to the best of your ability.
Prevention isn’t always possible. In the worst-case scenario, all you’ll be left with is treatment. Now, the difficulty with treating fungal infections lies in how fungi attack. This is true for most species of fungi. The trouble is that fungi is one of the most elusive types of infections because the bulk of what we call the mycelial network is underground or hidden in your plants. Fungi like Armillaria hide underneath the bark of your hibiscus shrub’s stems. Not only does this make it difficult to spot fungal infections, it also makes them incredibly difficult to treat.
You can, however, treat Armillaria root rot with various fungicides. The efficacy with which this can be accomplished will vary depending on the depth of the infection and the voracity of your treatment. Unfortunately, you’ll have to use fungicide for years to come given that these fungal infections persist for decades underneath the ground. However, if you can eradicate the mycelial fans, destroy the mushrooms, and clear your hibiscus plant’s immediate surroundings of any rhizomorphs, you should be fine.
This is, however, incredibly difficult to do, and we’d suggest that you should you find your garden infected with Armillaria root rot, you should dig infected plants up and start over. A really good way to stop something like this spreading is to instead use planters or pots for your hibiscus plants, as each plant will have a semi-enclosed environment that you can place into a sort of quarantine should you need to.
You may not recognize this fungal infection from its (slightly) scientific name, but you’ll know it when you see it. This, ladies and gentlemen, is gray mold. Even I’m breathing a slight sigh of relief here because this is a species of fungus that you actually stand a chance against.
Essentially, Botrytis blight resembles the mold that grows on fresh food when it comes into contact with airborne spores and a high enough level of moisture. Botrytis blight isn’t fun to deal with, but it can be eradicated. The best part about this particular fungus is that it doesn’t attack woody parts of your hibiscus, it only goes for soft, supple matter. We’ll get to why this is a good thing a little later.
How does Botrytis blight work?
Like most fungi, Botrytis starts out its life as airborne spores ejected by mature fungi. From there, the spores float through the air and attach to nutrient-rich sources in moist environments. In this case, the environment would be a slightly overwatered hibiscus plant.
Botrytis only affects soft fleshy parts of your plant and won’t attack the woody regions. It’ll attach first to either a leaf or a flower, and from there it’ll spread to the rest of the plant, if untreated.
Like Armillaria, Botrytis is both a pathogen and a saprobe. This means that the fungus may start off by attacking healthy tissue, but it will also feed off of decaying tissue. Once the infection sets in, it typically takes a few days for Botrytis to attack the entire flower, leaf, or other soft parts of your hibiscus plant.
How to identify Botrytis blight
This is a relatively easy fungal infection to identify. The first sign that your hibiscus is infected with Botrytis spores will most likely be translucent patches on its petals, sepals, and leaves. These will often look like wet spots, and are similar to the visual cues of an overwatered hibiscus plant. These translucent wet spots are where the spores first touch down and where they begin their assault.
It takes anywhere between a few hours and a few days for the first signs of mold to appear, but once it does, you’ve already got a thriving little colony of Botrytis fungi with which to contend. This is due to how the Botrytis fungus works.
What you see is a thin coating of patchy white or gray mold. It looks relatively fluffy or fuzzy, and the tissue around the molded area usually looks less than healthy. What you’re actually seeing is a microscopic forest of Botrytis. Even though it looks like the mold is just coating the surface of your plants, by the time you see the so-called gray mold, the infection is already far deeper than just the surface.
The way fungi proliferate is that the spores settle on the surface of healthy tissue. As soon as the spores are settled, the next part of the invasion begins. Microscopic filaments called hyphae start penetrating the surface of your plant’s soft tissue and grow deep into its innermost structure. These hyphae form an interconnected network with other spore drops called the mycorrhizae.
The mycorrhizae is something that we’ll discuss at length at the end of this article, but for now, all you need to know is that the infection runs really deep; deeper than what you see as the thin layer of fluffy mold. This is why it’s so difficult to get rid of mold like this. Once it attacks, it’s impossible to save individual parts of your hibiscus plant. Instead, your primary concern should be to save the core parts of your plant.
How to manage Botrytis blight
There are two ways in which you’ll manage Botrytis blight. First, you’ll try and prevent it from settling on your plants in the first place. We’ll discuss that in greater detail below. However, once an infection sets in, you’ll want to cut away any infected parts to ensure that the infection doesn’t spread, and you’ll need to take measures to make sure that your plant recovers and thrives. Let’s discuss preventative measures first.
The most important thing to remember about fungi is that in most cases, it is inherently predisposed to seek out moisture and warmth. Therefore, the best way to protect your plants against fungal attacks is to control their moisture as best as you can. This is particularly important in the case of something like hibiscus as this plant doesn’t like waterlogged soils or wet feet in any case.
The next thing is to ensure that your hibiscus plant gets enough sun. Hibiscus is typically meant to receive between 6-8 hours of direct sunlight a day. This helps to ensure that your plant has time to dry out between waterings and that it doesn’t grow in the shade, where moisture and mushrooms lurk.
Should you find lesions or wet spots on your hibiscus plant, the best course of action is to remove the afflicted area. It’s unlikely that you’ll be able to save individual blooms or leaves, but you can still save the plant. Given that hibiscus grows back fairly quickly and profusely, should you be in the right season, the easiest way to save your plant would be to prune it.
The correct season to prune hibiscus is Spring, but, as we discuss in our seasonal guide, you can also prune your plant during summer and the beginning of fall, depending on your climate. You can cut your hibiscus plant back as much as a third of the size of the original plant, if need be.
As a final deterrent for future gray mold, you may want to use either chlorothalonil, triforine, or thiophanate methyl. These are all fungicides that you should preferably apply to your hibiscus plant before a fungal infection develops. However, also keep in mind that not all gray mold are equal, and, some species are more resistant to fungicides than are others. This is particularly true when the conditions in your garden are the perfect breeding ground for fungi.
Leaf spot disease
This isn’t so much a particular type of fungal infection, but more the physical condition that many types of fungal infections cause. Leaf spot disease is often the earliest sign that your hibiscus plant is being attacked by a fungus. These spots range in color from yellow to brown and are usually relatively hard to the touch.
The physical spot is usually the location where fungal spores first touch the surface of your hibiscus plant. The spots are also, therefore, the place where decay first starts. You’ll notice the surface of your plant around each spot looks a little dead and dry. This is because the fungal infection is sapping your plant of its nutrients. There’s a reason why fungus does this, but we’ll get to that a little later. The most important thing to keep note of is that these leaf spots are proof that a fungus of indeterminate nature is killing your hibiscus’ leaves.
There are cases in which leaf spot disease has been attributed to bacterial pathogens and insects, but these are far rarer than the usual culprit, fungus.
How to treat leaf spot disease
We’ve already explained what leaf spot disease is and what it looks like, so we’ll just jump right into how to treat it.
It’s pertinent to note that in many cases, your plant is stronger than the fungus causing the leaf spots. Usually, leaf spot disease affects a few leaves and then gradually dissipates when the leaves die. This is because the fungi that cause leaf spots are most commonly surface dwellers like Botrytis. We call these surface dwellers, even though they build networks deep within your hibiscus plant’s innermost structure, because they don’t form vast underground networks that can extinguish entire plants.
Usually, if you find spots on a hibiscus leaf, only that leaf contains the hidden microscopic mycelial network of hyphae and mycorrhizae. There’s no larger network under the roots of your plant that is slowly suffocating the plant of all its nutrients. Even if other fungal infections are present, those that cause spots on a few leaves are usually only localized to those leaves.
Now, if your entire plant is covered in leaf spots, there is likely a larger, more virulent, and destructive fungus at work. But this isn’t always the case.
The easiest way to eradicate this type of damage is to remove the leaves that present with leaf spots. Simply take them to clean off of your plant and dispose of them away from any other plants. Remember, spores travel.
If you’re looking for a way to prevent fungi from causing leaf spots, only water your hibiscus plants when it’s warm, and they have enough time to dry properly before the cold weather sets in.
Phytophthora rot is a type of fungus that attacks plants, causing a disease known as phytophthora root rot. It is a particularly destructive disease that affects a wide range of plants, including hibiscus. This particular fungus is just as destructive and virulent as Armillaria root rot, and because it attacks the root of your hibiscus plant, it also operates in a similar manner to that first fungal infection we discussed.
Neither of these are a pleasure to have in the garden, and both are incredibly difficult to eradicate in their entirety because they can thrive in the soil below dead and decaying biological matter for a very long time.
How does Phytophthora root rot work?
The life cycle of the fungus responsible for phytophthora root rot begins when it releases its spores from infected plants or from the surrounding soil where they grow after prior infection. These spores spread easily through water, wind, or with the assistance of insects or other animals moving about within your garden.
As soon as these spores come into contact with a suitable host plant, such as your hibiscus, they germinate and form a root-like structure called a haustorium. When dealing with fungus, you learn a whole lot of new and exciting words, and haustorium has to be one of the coolest words that I’ll never be able to use in normal civil conversation. Such is the double-edged sword we call mycology.
The haustorium is basically a thin tendril that shoots from the responsible mycelium’s hyphae and attaches itself to the roots of your hibiscus plant. This is the bit of the mycelium that is responsible for nutrient transfer between plants, another aspect we’ll discuss after this article. The haustorium is perfectly suited to and capable of penetrating the roots of your host hibiscus and establishing itself within your plant’s tissues.
Once inside the plant, the fungus begins to grow and reproduce, spreading through the plant’s vascular system and causing damage to the plant’s tissues. As has been the case with most of the fungi we have discussed up to this point, this particular little blighter is both a pathogen and a saprobe.
As the fungus spreads, it begins to produce more spores, which it will happily release back into the soil or water to infect other plants. Phytophthora root rot and the fungus that causes it does not play around when it comes to seeking out and destroying live tissue in your garden.
How to identify Phytophthora root rot
Hibiscus plants infected with phytophthora rot often show symptoms such as yellowing and wilting of leaves, as well as dieback of branches. This means that your plant will look really rough and scraggly shortly after the infection takes root, and you’ll know just by looking at your hibiscus that there’s a massive problem.
The fungus can also cause the roots of the plant to become black and rotten, leading to the death of the plant. Now, looking for blackened roots will require you to dig around in the dirt for a bit, but this is just a way to ensure you know what the problem is. Don’t disturb your hibiscus’ roots without good reason. If you see your hibiscus is struggling, root around in its roots; if not, leave the roots alone.
Phytophthora root rot attacks hibiscus plants by entering through the roots and spreading throughout the plant. It is able to survive in soil for long periods of time, making it a particularly difficult fungus to control, as we discussed previously. However, such things sometimes merit a second mention.
To identify phytophthora rot in hibiscus plants, it is important to look for the symptoms mentioned above, as well as for the presence of a white, cottony growth on the roots. This is basically a nightmare fungus.
How to manage Phytophthora root rot
Preventing phytophthora rot in hibiscus plants involves several key strategies. You’ll notice that these preventative strategies are very similar to those we discussed in previous sections. The thing to keep in mind is that most fungus spreads in a similar way and requires similar conditions.
Therefore, preventative measures are often more of a blanket statement and not a set of different instructions for differing species. These preventative measures include:
- Planting hibiscus in well-draining soil
- Avoiding over-watering or allowing the soil to become waterlogged
- Avoiding planting hibiscus in areas with a history of the fungus
- Using a soil sterilant when planting hibiscus
If phytophthora root rot is already attacking a hibiscus plant, it can be difficult to eradicate. The infected plant should be removed and destroyed to prevent the fungus from spreading to other plants. In addition, the area around the infected plant should be treated with a fungicide to kill any remaining fungus in the soil. See? I told you it was similar to Armillaria root rot. Overall, phytophthora root rot is a serious threat to hibiscus plants and requires careful attention to prevent and control.
By following preventative measures and taking prompt action if the fungus is detected, it is possible to protect hibiscus plants from this destructive disease. However, I do want to stress one last time that if you find this particular fungus in your garden, you’ll need to destroy the affected plants and dispose of them away from your other plants.
The next condition we’ll discuss is powdery mildew. Now, to be clear, powdery mildew isn’t so much a fungal infection on its own. It’s more the visual effects of various fungal infections caused by numerous fungal culprits. These culprits include types of fungi such as Erysiphe cichoracearum, Podosphaera xanthii, and Sphaerotheca fuliginea.
These names might not mean much to you unless you’re studying mycology, but it basically just goes to show how common a visual attribute powdery mildew is where mycelia are concerned.
Hibiscus plants infected with powdery mildew often show symptoms such as white, powdery spots on their leaves, stems, and flowers. The fungus can also cause the leaves to become distorted and yellow, and can lead to the death of your plant if left untreated. The lesson here is don’t leave powdery deposits on your plants untreated.
How does powdery mildew work?
The short answer here is it works very well as a dispersion tactic for the responsible mycelia. Powdery mildew attacks hibiscus plants in the same way that most other mycelia do; by penetrating the plant’s innermost tissues and feeding on its cells. The fungus reproduces by producing spores, which it then spreads to other plants by way of wind or water. In some cases, fungi can spread by way of pollinators or other little critters roaming around your garden, but with something like powdery mildew, it’s primarily spread by the natural elements. Spores love to spread, and when there’s wind and water involved, they spread like wildfire.
How to identify powdery mildew
Becuase powdery mildew is but one visual cue of many types of fungal infections, how to identify it is quite simple. All you need to do is look for signs like a powdery white substance on your hibiscus plant’s leaves. Powdery mildew is also a way for fungi to take up nutrients from a plant. Therefore, you may also see evidence of decay and general structural damage. As previously mentioned, yellowing and wilting of the leaves are also a clear indication that there’s a fungal infection of sorts.
How to manage powdery mildew
As with most signs of fungal infection, there are several key aspects of prevention and treatment. We’ll look at prevention tactics first. These typically include:
- Planting hibiscus in well-draining soil
- Avoiding over-watering or allowing the soil to become waterlogged
- Providing adequate air circulation around the hibiscus plants
- Avoiding planting hibiscus in areas with a history of the fungus
- Using a fungicide as a preventative measure
However, sometimes it’s too late for preventative measures and you have to jump straight into treatment. If powdery mildew is already attacking your hibiscus plant, it can be rather difficult to eradicate. There are, however, a few things you can do. The first thing that needs to happen is that the infected plant should be treated with a fungicide according to each particular product’s instructions. Additionally, it is also of utmost importance to remove and destroy any infected plant material to prevent the fungus from spreading to other plants. Let’s be clear here again. If the fungus causing the powdery mildew is able to spread, it will.
I find it’s always best to either put the affected plant into a bin bag and toss it in the bin, or put it out with your other garden refuse. If you’re feeling a little viking you could burn it if you have a safe and well ventilated space within which to do so. It is also advisable to treat the area around the infected plant with a fungicide to kill any remaining fungus in the soil.
The truth about fungal infections
At this point, we’ve discussed five different fungal infections that can and will attack your plants, given the opportunity. However, simply discussing how bad fungi are for your garden does not – and should not – satisfy the broader horticulture industry within which I find myself writing. I understand that we are a website that focuses on bonsai and alchemy. But what is more magical than fungi?
This is a class of organism that we don’t even fully understand ourselves yet. The brightest minds in the field can’t agree or decide on whether fungi are animals or plants. And, who could blame them? What we have here is such a complex organism that functions in such mysterious ways that we don’t understand where in the natural order of things it fits. The one thing that we do understand, however, is that fungi are incredibly important for the environment and everything that exists within it.
Even though some types of fungi, like canker and mildew, are dangerous to humans and animals, many more species are essential to the balance of life on earth. In the future, I’d like to write a piece concerning fungi, particularly now that I’ve found a way to create bonsais from mushrooms.
For now, though, I’ll leave you with this; fungi may not be great to see attacking your plants, but all they’re doing is turning organic tissue into nutrients for other organic lifeforms to thrive on. Fungi are the good guys. Honestly, if you examine the delicate ecosystem of your garden more closely, you’re likely to find that there are very few clear-cut bad guys roaming around.
Everything has a place and a purpose, and there’s beauty to be found in it all.